A linear mechanical lock has a rod axially movable through a lock housing, and one or more coil springs, called clutch springs, tightly wound about the rod and axially fixed to the housing so as to normally grip the rod against movement through the housing. A release partially unwinds the coil spring or springs such that the internal diameter of the spring is increased and the rod is released for axial movement relative to the lock housing.
Linear mechanical locks are widely used in recliner seats used in automobiles and other vehicles. In such installations, the housing of the linear mechanical lock is attached to either the reclinable seatback or the stationary seat, while the end of the rod is connected to the other of those two seat components. In its normally locked condition the device fixes the position of the seatback. If the occupant desires to reposition the seatback, the lock is manually released, which frees the rod and allows movement of the seatback. The linear mechanical lock typically has a heavier exterior coil spring, called a return spring, which returns the rod to an extended condition when the lock is released. For example, the restoring spring may serve to bring the seatback to a fully upright condition.
In applications with bi-directional loading of the rod, two clutch springs may be provided, one on each side of a common release lever and axially contained between two end bushings. Each bushing engages an end tang of a corresponding spring to fix the tang and the outer end coils of the spring against rotation about the rod. The inner end coils of the springs are connected to a release lever. The release lever, when actuated, can simultaneously unwinding both springs to free the rod for axial movement through the housing.
The bushings serve at least three distinct functions. The bushings are annular, with an axial bore. An inner radial bearing surface supports the rod, allowing the rod to slide through the lock housing. A radial slot in the bushing receives an end tang of the clutch spring, to circumferentially fix the outer end of the spring and prevent this end of the spring from turning about the rod. Finally, an axial bearing surface on the bushing is circumferentially spaced by 90 degrees from the clutch spring tang. When the clutch spring is pulled with the rod against the axial bearing surface by a load acting on the rod relative to the lock housing, the end coils of the clutch spring are canted relative to the rod axis. This canting deforms the coils from a normal circular shape to an ellipsoid shape, and substantially increases the frictional engagement between the clutch spring coils and the rod. The clutch spring better resists the load and makes for a more positive lock of the rod relative to the housing so long as the loading condition persists.
In order to distribute the unwinding action more evenly over the length of the spring, one or more tubular sleeves may be used. A tubular sleeve envelops the clutch spring or springs, insuring that the coils unwind uniformly, rather than unwinding solely at the end with the release lever. Such a sleeve improves performance, allowing for quick release action of the lock.
During fabrication, the relative positions of the lock elements in the housing is rather critical and a high degree of precision must be maintained in assembling the lock. As a result, the fabrication and utility of the housing are critical. Many locks of this sort require components to be assembled inside a housing prior to the housing being bent or formed into its final shape. Such a process leads to a high degree of fall-out at all portions of the product life cycle.
The global automotive market is exceptionally competitive, meaning that automotive manufacturers are constantly striving for the seemingly contradictory goals of improved features, less expense, lighter weight, higher reliability, and more durability. As a result, linear mechanical locks used in adjustable and reclining seats not only need to be able to support a substantial load, but also be inexpensive, lightweight, reliable, and durable. Moreover, because of how they are used, locks used in vehicle seating have to account for both kinetic and static loading requirements.